First time around Dems would probably vote Dems 99, GOP 0 and leave every other party blank, but over time people would realise that you can ALSO score your actual favourite (think of all the people that would vote Green if it wasn’t a wasted vote) a 99 without hurting the “lesser evil’s” chances. Greens 99, Dems 99 and GOP 0 is just as bad for the GOP as Greens blank, Dems 99 and GOP 0. That’s the magic of score voting. And people who are really apathetic and refuse to vote because they think all parties are bad could still express an opinion akin to Dems 10, GOP 0, rest empty.
These are different ways to fill the same ballot! In score voting you give every party a score (in this case from 0 to 99). This was the example of a die-hard Democrat. A more moderate voter might vote something like Dems 50, GOP 60, or Dems 30, GOP 25